International Concrete Abstracts Portal

Describes the seismic rehabilitation methods for the reinforced concrete substructures of two structural steel bridges in California, the South San Francisco Overhead Bridge and the Los Angeles River Bridge. The rehabilitation is part of the seismic retrofit program implemented by the California Department of Transportation (Caltrans) after the 1989 Loma Prieta earthquake. The analysis and design basically followed the general seismic retrofit principles and guidelines developed by Caltrans and other research institutes in recent years. However, due to the site conditions and retrofit limitations of these two bridges, innovative methods were employed to minimize the retrofit costs.

The catastrophic collapse of the old Cypress Viaduct during the 1989 Loma Prieta earthquake emphasized the vulnerability of elevated freeway bridge structures. One track of the joint Caltrans and University of California, Berkeley, research project is the investigation of outrigger knee joints found in elevated freeway bents. This project has two principal goals: to evaluated the behavior of the existing outrigger knee joint subassemblies under a combined transverse and longitudinal loading and to devise and experimentally verify upgrading strategies and repair techniques suitable for application on the existing elevated freeways. The performance of the existing outrigger knee joint subassemblies was evaluated by testing two as-built models. After considering several upgrading strategies, two were tested on the remaining five specimens. In parallel with the experiments, a set of tools was developed for design and analysis of the upgraded subassemblies. A summary of the design, analytical, and experimental work conducted to date is presented in this paper.

Simply stated, shotcrete is sprayed concrete or mortar. Because of difficulty in obtaining good compaction and fully encasing large or closely spaced bars, it has traditionally been used in thin, relatively lightly reinforced sections. Unique to seismic repair and retrofit are heavily reinforced and often thick sections. Because of its ease of application in areas of poor access and the resulting reduction in construction time and cost, the process can be especially advantageous in seismic applications. Special procedures are required, however, to obtain good quality work under the common inherent constraints that often exist and overcome the limitations. Although not widely recognized, proven procedures are well established and have been successfully used in seismic repair and retrofit applications for nearly 50 years. Basic principles of the shotcrete process are reviewed in this paper; those special procedures required for proper placement in heavily reinforced and thick sections are discussed.

SP160 This publication brings out a wide spectrum of the state research and practice in the rehabilitation of concrete structures for improved earthquake resistance. It also covers seismic rehabilitation with regard to elements of the structures as well as the whole structure.

Inadequate shear strength and inadequate lap splices in the longitudinal reinforcement are two major deficiencies in non-ductile reinforced concrete columns. Such deficiencies limit the lateral strength and ductility of older reinforced concrete moment-resisting frames. Provisions of older codes led to columns with shear strength less than required to develop the member's flexural capacity. Consequently, non-ductile shear response may dominate the behavior of older short columns. In addition, lap splices in older concrete columns were primarily designed as compression splices, but may actually experience large tensile forces during earthquakes. As a result, lap splices in older concrete columns are often inadequate to develop the yielding strength of the spliced bars in tension. This paper presents results of an experimental investigation on the use of rectangular steel jackets for seismic retrofit of rectangular reinforced concrete columns with inadequate shear strength or inadequate lap splices. Three large scale columns with inadequate lap splices and four large scale columns with inadequate shear strength were tested under lateral cyclic loading. The basic unretrofitted columns showed early dramatic non-ductile failures. However, the retrofitted columns with steel jackets exhibited excellent response, higher strength, and much higher ductility and energy dissipation. Test results suggest that rectangular steel jackets can considerably improve the performance of columns with inadequate shear strength. Also, the steel jackets can significantly enhance the response of wide columns with inadequate lap splices, when stiffened with adhesive anchor bolts.